Evaluating the joinability of thin-walled high pressure die cast aluminium for automotive structures using self-piercing rivets

Abstract

This paper is the first to report successful application of self-pierce riveting (SPR) in thin-walled high pressure die cast (HPDC) aluminium for use in automotive applications. HPDC fabricated AA356x coupons were joined to conventional rolled RC5754 material. A set of industry-relevant joint stacks were created. Priority stacks included cast material as the upper layer. More challenging joints were also fabricated with cast material as the lower layer. Automotive industry key performance indicators were used to assess joint integrity. The key results and recommendations were: • HPDC aluminium was revealed to be able to be joined to rolled aluminium according to vehicle manufacturer automotive standards. • Process boundaries were established for satisfactory SPR joints across a range of material thicknesses and stack types. • SPR joint solutions were proven in the most challenging stacks with cast material as a bottom layer. • Greater variability in the joint key performance indicators was observed in stacks where the cast alloy is the top layer. • Microstructural analysis of both AA356x and RC5754 revealed differences in grain structure and hardness and it is proposed that this accounts for the increased variability. • Strength testing of lap shear joints demonstrated the mechanical effectiveness of an SPR joint including cast material. Under normal vehicle operating conditions, the performance of joints including cast material was equivalent to that of rolled material only joints. Following yielding, joints including cast material suffered a more brittle failure mode leading to differences in performance under crash scenarios.

Keywords

• Aluminium
• High pressure die casting
• Self-piercing rivets
• Automotive joining